1. Field of the Invention
The present invention relates to a production process of a display device, and a display device, and specifically relates to a liquid crystal display device using a vertical alignment mode which has excellent image display quality and other advantageous properties.
2. Description of the Related Art
A liquid crystal display device is in widespread use as a display of a household electrical appliance such as a personal computer and a television set. In the liquid crystal display device, a liquid crystal panel is used. The liquid crystal panel is produced by stacking and bonding two supporting substrates via a sealing member, in which the supporting substrates are insulating substrates and patterns are formed on the supporting substrates by a predetermined method, and then by filling a space surrounded by the sealing member with liquid crystals.
For the liquid crystal display device as described above, a device using a vertical alignment mode is commercially practical, in which a liquid crystal layer possessing negative dielectric anisotropy is interposed between an opposed supporting substrate pair so that liquid crystal molecules are aligned vertically, and when a voltage is applied to the liquid crystal layer, the liquid crystal molecules are controlled to be aligned in a plurality of inclined directions relative to the supporting substrates.
In this liquid crystal display device using the vertical alignment mode, in order to improve viewing angle characteristics in display, it is effective to create a plurality of domains in one pixel for controlling the liquid crystal molecules aligned in the vertical direction to be aligned in a plurality of inclined directions that are different from one domain to another relative to the vertical direction. For this purpose, as control mechanism for liquid crystal molecule alignment for creating such domains, a linear protrusion is provided to a common electrode on the substrate at a color filter side, or an opening is provided to a pixel electrode on the substrate at an active element side.
FIG. 7 is a plan view showing linear protrusions 81 in two pixels adjacent to each other, which are formed on a substrate at a color filter side. The linear protrusion 81 is formed by deposition of materials, a photolithography process, and development. To be specific, a photosensitive organic insulating film is coated on a common electrode 85 to be subjected to a pre-baking process, followed by an exposure process. After the exposure process, the insulating film is developed with a developing solution to remove unnecessary portions, and a pattern of the linear protrusion 81 is formed as shown in FIG. 7.
In recent years, accompanied by upsizing of a screen for a liquid crystal display device used in a liquid crystal television set and the like, a manufacturing apparatus which is usable in manufacturing a large-sized screen has been required. However, concerning exposure, a conventional small-sized lithography is used in manufacturing the large-sized screen by using divisional exposure such that a screen is divided into a plurality of regions to be exposed.
A procedure for forming the above-described linear protrusion 81 by such divisional exposure is explained referring to FIGS. 7 to 9D. The chain double-dashed line in the middle of FIG. 7 indicates a boundary 80 for divisional exposure. FIGS. 8A and 8B are magnified views showing two division masks 82 and 83 used for divisional exposure in a circled portion D of FIG. 7. FIGS. 9A and 9B are sectional views showing states at a section E-E of FIGS. 7, 8A and 8B in the course of divisional exposure using the division masks 82 and 83.
First, the organic insulating film 84 that is a positive photoresist is coated on the common electrode 85 to be subjected to a pre-baking process, followed by the exposure process using the division mask 82 shown in FIG. 8A. As shown in FIG. 9A, the division mask 82 includes opaque patterns 82a and 82b for patterning linear protrusions 81b and 81c on the right side of the divisional boundary 80 and an opaque pattern 82c on the left side of the divisional boundary 80, and transparent patterns 82d, 82e and 82f. As illustrated, the transparent patterns 82d, 82e and 82f provide diffraction light K, which forms exposed portions 84a, 84b and 84c in the form of an inverted trapezoid in the organic insulating film 84.
Next, the exposure process using the division mask 83 shown in FIG. 8B is performed. As shown in FIG. 9B, the division mask 83 includes an opaque pattern 83a for patterning a linear protrusion 81a on the left side of the divisional boundary 80 and an opaque pattern 83b on the right side of the divisional boundary 80, and transparent patterns 83c and 83d. Also in this case, the transparent patterns 83c and 83d provide diffraction light K, which forms exposed portions 84d and 84e in the form of an inverted trapezoid in the organic insulating film 84. In this instance, a portion 84f at the divisional boundary 80 is double exposed.
Then, after the development with the developing solution is performed and the exposed portions are removed, the linear protrusions 81a, 81b and 81c are formed as shown in FIG. 9C.
As a prior art literature relating to the present invention, Japanese Patent Application Unexamined Publication No. 2003-322864 is cited.
However, since the linear protrusions 81a and 81b in the vicinity of the divisional boundary 80 are close to each other as shown in FIG. 9C, if exposure displacement is caused by an error in stitching the divided regions, the linear protrusion 81b in the right side is unintentionally formed to be thin as shown in FIG. 9D or disappears at worst because of the double exposure. Such thinning or disappearance of the linear protrusion 81b that is the control mechanism for liquid crystal molecule alignment leads to poor alignment of the liquid crystal molecules in this portion, resulting in a problem that unevenness occurs in and around the divisional boundary.
Such an error in stitching the divided regions is caused by an alignment error of the masks, a magnification error, a dimensional deviation in manufacturing the masks, or the like. However, improving accuracy thereof causes a great increase in the cost of the lithography, leading to a cost problem.